1. Field of the Invention
The invention presents to a novel method to produce an excellent storing energy device, enhancing the efficiency of manufacture and the reliability of products particularly for the bipolar ultracapacitors. Two main problems to the bipolar assembling devices are the electrolyte leak of the sealed device and the unequal voltage among the accumulating cell units. The invention can thoroughly solve the problems as well as limitation of mass production and constitute a highly reliable and efficient element of storing energy.
2. Description of Related Art
Among devices of storing energy, the two representative components are batteries (such as lithium cell and Ni—H cell) and capacitors (such as aluminum electrolytic capacitor, ceramic capacitor or tantalum capacitor). Batteries are typically low power devices whereas conventional capacitors may have a power density of 106 watts per dm3 at a very low energy density. Ultracapacitors are devices with energy storage density and power density intermediate between capacitors and batteries. Thus, ultracapacitors may improve battery performance in terms of power density or may improve capacitor performance in terms of energy density when combined with the respective device. In addition, ultracapacitors are expected to have a much longer cycle life than batteries because none or negligibly small chemical charge transfer reactions are involved.
Ultracapacitors may be classified into two groups, namely, electric double-layer capacitors (EDLC) and pseudo-capacitors. The former stores electric charges at the double-layer formed at electrode electrolyte interface. Electric charges of the latter are stored mainly in the electrode surface region by faradaic reactions, with energy density 5-10 times of the electric double layer.
In general, there are three kinds of material of electrodes applied in ultracapacitors: carbonaceous material, metal oxide and conductive polymer. The main electrode materials of carbonaceous ultracapacitors, the representative of double layer, are active carbon, glass carbon or active carbon fiber cloth. The mechanism of storing energy is made of the isolated electric charge on the interface between electrode and electrolyte of electric double layer. As for pseudocapacitance, there are two kinds of material of electrode: the metal oxide (such as, RuO2, IrO2, Co3O4, MoO3, WO3 and molybdenum nitride) and conductive polymer (such as, polyaniline, polypyrrole and polythiophene.) There are three methods for constructing an ultracapacitor. The first one is wind type, utilized by many carbonaceous ultracapacitors. The advantage for winding ultracapacitors is that the electrode area is enormous whereas the connection between units of ultracapacitors, the volumetric density with high voltage ultracapacitors and connection between electrodes are disappointing. The second method is stacked type. The advantage is that the units are easily constituted to series connection and stacking density of the piles is high. The third one is bipolar stacked type, using the oppositely two sides of electrode for the positive and negative poles. It obtains easily high voltage and is organized efficiently and its volume is easily reduced, which can reduce the manufacturing cost. However, this method requires the isolation of electrolyte between the units and is thus more difficult. The key problems of encapsulation are the electrolyte leak and the unequal voltage of accumulative units. The technical level for mass production is much higher than the wind and stacked types. For the details, refer to the patents of U.S. and of TW: U.S. Ser. Nos. 06/005,764, 05/867,363, 05/384,685, 05/464,453 05/980,977, 06/174,337, 05/800,857, 05/821,033, 05/711,988, TW 283273 and TW284921.
As shown in FIG. 1, the unit cell of the ultracapacitor (10) comprises two electrically conducting flat sheet (11) coated on a high surface area material as the electrode (12), ion permeable or semipermeable separator (14), immersed by electrolyte, and then packaged by encapsulant (13). The electrolyte may be aqueous or organic. The aqueous solution offers low internal resistance but limits the voltage to 1 volt. In contrast, the organic electrolyte allows 2.5˜3V volts of charge, but the internal resistance is higher.
The working voltage and capacitance of the unit can be enhanced by series and parallel connections. To operate at higher voltages, ultracapacitors are connected in series. On a string of more than three capacitors, voltage balancing is required to prevent any cell from reaching over-voltage. Numberless ultracapacitors can be in series connected by circuit. However, for ultracapacitors with high voltage, the circuit system needed is huge. Furthermore, in order to ensure the reliability of the whole ultracapacitor, the balanced circuit must be added between the individual units. These make ultracapacitors disadvantageous in the respects of volume, weight, cost and manufacture.
Among other methods to enhance the working voltage of ultracapacitors, the adherence is more efficient, which in series connects ultracapacitor units by the adherence of silver or conductive gels. For a detailed description of this, refer to TW. Patent 472271. The electrolyte is filled in a proper interspace between the two electrodes to form a single unit. Then a few units made in the same way are adhered and accumulated to each other. FIG. 2 shows the storage energy unit. FIG. 3 shows the accumulation of units. Each of them is adhered by silver or conductive gels, similar to the series connection of unit. Finally, the accumulation of units is packaged by a container to form an ultracapacitor with high voltage and the material of the top and bottom of the container is elastic and conductive. Although this method is better than the circuit of series connection, the silver or conductive gels will decay in the process of charge and discharge, which decreases the reliability of the ultracapacitor. Besides, the efficiency of the electrode plates is far worse than that of the structure of bipolarity.
The structure of bipolarity is the most efficient for series connection. The method uses the oppositely two sides of each electrode plate for the positive and negative poles at the same time. Every unit can be closely in series connected to each other. The usage of electrode plates is around half of the adherent series connection. For example, the adherent series connection with 100 V needs 200 pieces of unitary electrode plate with 1 V. However, the bipolar one only needs 101 pieces of that. The characters of bipolar series connection are that the physical and electrical properties of each unit are equal and that the electrolyte of each unit is isolated.
The one shown in FIG. 4 is a conventional bipolar ultracapacitor structure 20. (For a detailed description, see U.S. and TW. Patents: U.S. Ser. Nos. 06/005,764, 05/867,363, 05/384,685, 05/464,453, 05/980,977, 06/174,337, 05/821,033, 05/711,988, TW 283273 and TW284921.) The ultra capacitor has an upper conductive plate 211 and a lower conductive plate 212 on the top and the bottom for connecting outside electricity. The proper amount of electrodes 22 is directly to be accumulated to a dry pre-structuring unit. A cord 23 is used to make a beforehand port 24 of the dry prepared unit. There is a gasket between each electrode and then the fillport is filled with the electrolyte. Finally, the structure 20 of ultracapacitor is finished.
However, there are serious defects in the packing method mentioned above in the efficiency of manufacture and the reliability of products. In the respect of reliability, to begin with, the connection of pores by three-dimension electrode causes the electrolyte leak. Second, the different distance of each electrode causes different height of each stored energy unit. An expansion or crack of the stored energy units may occur, as the units can't equally share the voltage when the ultracapacitor charges or discharges. The mass production may be inefficiency due to setup of the gasket, placement and extraction of the cord, the beforehand port and the adhesive binding.
The high capacitance of ultra capacitors mainly comes from the high surface area of the electrode. As shown in FIG. 5, the electrode pores can be alone or connected to each other by 2D or 3D structures. According to the size, the holes can be divided into micropores smaller than 10 μm, macropores bigger than 50 μm and mesopores between these two. The micropores are unavailable for the ultracapacitor mechanism of storing energy, whereas the mesopores are the most suitable ones. The electrolyte leak is due to the connection between each electrode pore by 3D. As illustrated in FIG. 5, the surface pore A of the electrode is easily blocked by the sealing gel but the edge and side pores of the electrode are difficult to block. Even though the electrode is spread around with the gel in order to allow the low viscosity gel to penetrate into the pores, as in the TW. Patent 472271, this method still can't prevent the leak of the sealed side. It is because that not all the pores vertically connect through the electrode. In the layer of electrode, some pores don't connect to the surface of the electrode but connect to the edge and side of the electrode. The electrolyte is leaked from these pore channels.
Besides, every unit has to share the same voltage under the operation of high working voltage. When the individually shared voltage exceeds what the unit can support, the capacitor begins to expand, leak and then crack. In order to let the units of ultracapacitor equally share the voltage, the structure of every unit must be same. The distance between every electrode is a very important parameter and is controlled by the gel-sealed wall or the gasket between the electrode. In TW. Patent 472271, the gel-sealed wall is used. The gel spread on the electrodes with pores and screen printing are used for the isolation of the electrode to control the height of the ultra capacitor units. As the gel-sealed wall is on the electrode pores with different depth, its thickness is hard to control. This results in different height of each unit and further influences the height of the multiple units. For example, if the difference in height for one unit is 10 μm, the difference for the ultra capacitor with 100 V will be 1 mm, which will cause serious influence on the average voltage of the ultracapacitor with high working voltage. In U.S. and TW. Patents: U.S. Ser. Nos. 06/005,764, 05/867,363, 05/384,685, 05/464,453, 05/980,977, 06/174,337 05/800,857, 05/821,033, 05/711,988, TW 283273 and TW284921, the unitary he is controlled by the gasket. This method also first lets the low viscosity gel penetrate into the electrode pores and then control the unitary height by using the gasket. However, the gasket loses its accuracy for the same reason—The thickness of the pores is hard to control due to the gel sealing. This makes the height of each unit different and further influences the distance between the units.